An approach for providing thermal barrier coating on a surface of a base material of a component is known to improve heat resistance of the base material. For example, in a gas turbine, an approach for providing thermal barrier coating on surfaces of a rotor blade and a stationary blade that are included in the turbine is known.
A member formed on a surface of a component by thermal barrier coating (hereinafter, “thermal barrier coat”) is generally composed of two layers: an external layer called a top coat, and a layer called a bond coat that joins the top coat and the base material together. In a thermal barrier coat for a gas turbine, a ceramic having low thermal conductivity is used as the top coat, and an alloy having excellent oxidation resistance is used as the bond coat.
When the thermal barrier coat is exposed to a high temperature for a long time, a thermally grown oxide (hereinafter, “oxide scale layer”) oxidized by the heat from the top coat, may be generated on the side of the bond coat facing the top coat. The oxide scale layer is generated on an area of the bond coat in contact with the top coat, and expands as thermal load applied to the thermal barrier coat increases. As the oxide scale layer expands and the thickness thereof increases, the oxide scale layer pushes up the top coat to, for example, form a crack on the top coat. As a result, the top coat may be separated from the base material and the bond coat.
To detect the separation of the thermal barrier coat in advance, an approach for estimating deterioration of the thermal barrier coat, that is, the degree of damage onto the barrier coat, is called for. In a technology disclosed in Patent Document 1, an impact force is applied to a thermal barrier coat. For example, a spherical object is collided thereagainst. Thus, the thermal barrier coat is destroyed, and information about deterioration of the thermal barrier coat can be obtained according to the condition of damage, such as the separation, provided thereto.    Patent Document 1: Japanese Patent Application Laid-open No. 2002-277383